Cationic Polyelectrolytes

Inflammation, Vol. 11, No. 4, 1987 CATIONIC POLYELECTROLYTES: A New Look at Their Possible Roles as Opsonins, as Stimulators of Respiratory Burst in Leukocytes, in Bacteriolysis, and as Modulators of Immune- Complex Diseases (A Review Hypothesis) ~ ISAAC GINSBURG Department of Oral Biology Hebrew University-Hadassah School of Dental Medicine "Jerusalem, Israel Department of Pathology The University of Michigan Medical School Ann Arbor, Michigan INTRODUCTION Voluminous literature exists today on the involvement of cationic polyelectrolytes (CPs) in host and parasite interrelationships. It has been shown that CPs of neutrophil (1-14), eosinophil (15, 16), macrophage (17), and platelet (18) origins function as distinct microbicidal agents. These probably constitute a "secondary" defense line supplementary to the main oxygen-dependent microbicidal systems of "professional" phagocytes. CPs have, however, also been implicated as modulators of blood clotting (19) and fibrinolysis (20), as a permeability-enhancing factors (21-23), in mast cell degranulation and in his- tamine release (24), as pyrogenic agents (25), as enhancers of complement- mediated lysis (26), as modulators of PMN adherence (27-29) and chemotaxis (30-34), and as modulators of endocytosis (35-45) to list only several of the properties ascribed to these agents. Since the effects of CPs probably involve the interaction, through electrostatic forces, with negatively charged sites on ~This study was supported in part by a research grant from Dr. S.M. Robbins of Cleveland, Ohio; by grant CA-36132 from U.S. Public Health Service awarded to Dr. James Varani, and by grants GM-29507 and P01-HL-31963 (Program Project) awarded to Dr. P. Ward by the U.S. Public Health Service, Parts of the work described in the review were performed by the author during tenure as a visiting professor at the Department of Pathology, University of Michigan, in 1985 and 1986. 489 0360-3997/87/1200-0489505.00/0 1987 Plenum PublishingCorporation 490 Ginsburg target cells (36), it is plausible that the complex polyelectrolytic milieu found in infectious and inflammatory sites might function to modulate and regulate several important interactions of the host with invaders (46-48). Although CPs are primarily recognized for their distinct killing properties (10-13), recent studies have suggested that CPs might also be involved in a variety of additional biological, biochemical, and immunopathological phenom- ena which are seldom discussed in the general context of host and parasite interrelationships. The present review deals primarily with the possible involvement of CPs (1) in endocytosis and in cell adherence, (2) as activators of the respiratory burst in "professional" phagocytes, (3) as activators of the autolytic wall enzymes in certain microbial species and its relation to bacteriolysis and to the patho- genesis of chronic inflammation induced by bacterial cell walls, and (4) as agents capable of modulating the pathogenicity of immune complexes. It was felt that a discussion of these "other" properties of CPs is timely as it may shed a new light on the role of surface charge in cell-to-cell interactions as seen in inflammatory and infectious sites. ROLE OF CPs IN ENDOCYTOSIS The very extensive literature on the role played by receptor-mediated phagocytosis by "professional" phagocytes in host defense against foreign invaders has been recently reviewed (49-52). In addition to immunoglobulins (Ig) and complement ligands, endocytosis may also be mediated by nonspecific recog- nition mechanisms (53), by "primitive agglutinins" known to be found in in- vertebrates (54), by lectins and natural peptides (55), as well as by extracellular matrix proteins (56). Both electrostatic and hydrophobic interactions have been implicated in the internalization (endocytosis) of both soluble and particulate agents (35-45, 51, 57, 58). The opsonic properties of the CPs were not necessarily related to their high bactericidal effects (36-38), as nonviable bacteria are also taken up by phagocytes. The efficiency of the CPs as opsonizing agents depended on their binding to the particle surface, on the length of the polymers, and on their net cationic charge (36). Usually, polymers with a molecular weight smaller than 4000 were not toxic and poorly opsonic. It is of interest, however, that nuclear histone at nontoxic concentrations proved to be an excellent opsonin despite the fact that only about 30 % of its amino acids are basic (see next section). Since CPs very efficiently opsonized highly encapsulated group C streptococci and Klebsiella pneumoniae, as determined by the capacity of the coated cells to induce chemiluminescence in PMNs (59), and since nonopsonized bacteria were not phagocytosed, it was suggested that CPs might also function as auxiliary opsonins Cationic Polyelectrolytes 491 in vivo. Although no direct proof to this effect is available in the published literature, preliminary observations (Ginsburg and Polatchek) suggested that Cryptococcus neoformans, which had been preopsonized in vitro by nonlethal concentrations of histone, caused a much milder infection in mice as compared with mice which had been infected by untreated yeasts. It is suggested that the cationized yeast cells were "recognized" by the mononuclear phagocytic sys- tem and were removed by phagocytosis. An unexpected observation on the role of CPs in endocytosis of yeast and bacteria by "nonprofessional" phagocytic cells was described in detail by Ginsburg et al. (42). Candida albicans, which had been preopsonized either with histone or with poly-L-arginine (PARG), adhered, within seconds, to monolayers of mouse L-fibroblasts, to human buccal epitelial cells, to HeLa cells, and even to beating rat heart cells. The yeast cells which attached them- selves to the cell membrane were later seen to migrate and localize in a rosette form around the nucleus. A few hours after attachment, endocytosis was ob- served. Electron microscope analysis of the cells revealed the presence of Can- dida within tight phagosomes. No fusion between phagosomes and lysosomes was evident, however. In many instances, a partial degradation of the yeast cytoplasm was seen, however, suggesting that lysosomal enzymes of the fibroblasts might have been responsible for this phenomenon (42). Nonopsonized Candida were never seen either attached to the cells or intracellularly. Under similar conditions, both histone and PARG-opsonized group A streptococci and M. lepraemurium were also avidly phagocytosed by mouse fibroblasts, but no signs of bacterial degradation were evident (Ginsburg, unpublished results). Nuclei of human U266 myeolma cells that had been preopsonized either with histone or with PARG were also avidly taken up by mouse L-929 fibroblasts in culture (64). The nuclei that were found within tight phagosomes had undergone a partial degradation 48 h following phagocytosis. As in the case of Candida, the nuclei first adhered very rapidly to the cell surfaces, but phagocytosis was evident only several hours later. Entamoeba histolytica, which failed to engulf either group A streptococci or Candida albicans, nevertheless avidly took up these microorganisms following in vitro opsonization by histone (65). Since fibroblasts have been shown to avidly take up (phagocytose) mast cell granules in culture (66), it is tempting to speculate that cationic agents released from the mast cells might have been involved in this process. More recent studies (Ginsburg and Varani, in preparation) have also shown that Candida albicans (Figure 1), group A streptococci (Figure 2) or E. coli which had been preopsonized either with nuclear histone or with poly-L-arginine were avidly internalized by fibrosarcoma cells in culture. Monolayers of fibrosarcoma cells which had been treated for short periods with cationized microorganisms to allow their adherence to the tumor cells and then challenged 492 Ginsburg Fig. 1. Phagocytosisof Candida albicans by mouse fibrosarcomacells in culture. Note the presence of yeast within phagocyticvacuoles (Giemsa stain, x 10,000). either by human or by rat neutrophils had peeled off the surfaces of the plastic dishes. The tumor cells, however, were not killed. Since scavengers of oxygen radicals did not prevent the breakdown of the tumor monolayers, but a variety of proteinase inhibitors did, it is suggested that proteinases released from the activated neutrophils were responsible for sloughing off the cultures. This phenomenon might explain how activated neutrophils could perhaps enhance tumor spreading. Tumor cells which had been treated with cationized streptococci and then challenged with neutrophils in the presence of sodium azide were readily killed. This suggests that inhibition of neutrophil catalase facilitated the accumulation of hydrogen peroxide which might have been responsible for killing of the tumor cells. A variety of CPs were found to inhibit the binding of human IgG to Fc receptors upon group A streptococci (67). While protamine and arginine-rich histone markedly inhibited the binding of IgG, neither lysine-rich histone nor egg-white lysozyme had any effect. This suggested that the arginine moieties of the CPs were more effective than the lysine ones. We also found similar results concerning the chemiluminescence-inducing properties of histone (68). CPs might, therefore, interfere with the uptake of Fc-bearing streptococci by phagocytes. The role played by CPs derived from PMNs in cell adherence and

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